| According to the invention,
the minimum compression ratio selected may be achieved between
two end-of-travel limits of the variably timed transmission.
The first limit is achieved with a maximum lead angle between
the crank of the short-stroke crankshaft [5] and the crank of
the long-stroke crankshaft [4], so as to determine at the end
of the compression phase ( top dead centre of piston [6] ) the
position of piston [8] with respect to the additional volume
required for the clearance space [40] to define said minimum
compression ratio with an angle of at least 90° between the
connecting rod and the crank of the short-stroke crankshaft
[5], the second limit is achieved with a smaller lead angle
between the crank of the short-stroke crankshaft [5] and the
crank of the long-stroke crankshaft [4], proportionally to the
reduction of the displacement ratio of the two cylinders [2]
and [3], up to the tolerance limit generated by the working
area of the two crankshafts [4] and [5], defined by the parallel
and close positions of the paired cylinders [2] and [3], according
to the following minimum compression ratio formula : |
|
V1 + [ V2 - Vr (α maximum)
] + ve
ve + Va (α maximum)
|
= P minimum |
It is possible to define a higher compression
ratio between the displacements of the paired cylinders, so as to
reduce the stresses on the variably timed transmission mounted on
engines having lower displacements and inversely, it is possible
to define a smaller compression ratio between the displacements
of the paired cylinders [2] and [3], so as to increase the speed
of engines having higher displacements. In practice, Vr (α
maximum) should not be deducted from V2, since the mass of air admitted
in V1 and V2 depends on the stored calibration between the compression
ratio and the supercharging pressure. The maximum compression ratio
selected is achieved on the basis of the dimensional values defined
for the minimum compression ratio, so that at the start-of-travel
of the variably timed transmission, the minimum lead angle between
the crank of the short-stroke crankshaft [5] and the crank of the
long-stroke crankshaft [4] determines, at the end of the compression
phase ( top dead centre of piston [6] ), the position of piston
[8] with respect to the additional volume required for the clearance
space [10] to define a maximum compression ratio, with the connecting
rod [9] of the crank of the short-stroke crankshaft [5] away from
its top dead centre, so that said connecting rod [9] forms an angle
with the crank of the short-stroke crankshaft [9]. The maximum compression
ratio may thus be defined by means of the following formula :
V1 + [ V2 - Vr (α minimum)
] + ve
ve + Va (α minimum)
|
= P maximum |
In practice, Vr (α minimum) should not
be deducted from V2, since the mass of air admitted in V1 and V2
depends on the stored calibration between the compression ratio
and the atmospheric depression in the intake pipe.
|
